1. Field of the Invention
The present invention relates to a semiconductor element sealing structure used mainly for sealing a semiconductor element such as a flip-chip mounted on a hybrid substrate, to prevent breakage of the chip or chip connecting portion and to allow an increase of the size of the chip.
2. Description of the Related Art
Heretofore, a semiconductor chip is sealed with silicone gel or the like to electrically insulate and protect the chip from environmental hazards such as water, shock, and vibration. In a hybrid IC (integrated circuit), a flip-chip, for example, is mounted on a conductor pattern formed on a thick layer printed substrate with soldering bumps formed on a main surface of the flip-chip. The flip-chip and the substrate are packed with silicone gel. The silicone gel entering a space between the flip-chip and the printed substrate is thermally expanded by the effect of the ambient temperature and self-generation of heat by various elements on the printed substrate, to pull up the flip-chip, and finally result in a breakage of the soldering bumps. We found that this phenomenon becomes more important as the size of a chip is increased, since the force pushing up the chip becomes larger.
Further, as is well known, silicone gels used for the above purpose contain unreacted vinyl groups and such vinyl groups will cause additional reactions with some ingredients of another addition reaction type silicone adhesive, for example, an adhesive used for adhering a cap to a case in which the chip has been sealed, and form additional cross linkages in the sealing silicone gel or increase the cross linkage density, thereby increasing the hardness of the silicone gel and thus accelerating the action of pushing up the chip. Silicone gels in which the hardness of the silicone gel will not change over a period of time, and in which the additional cross linking reaction of unreacted vinyl groups is improved, have been proposed. But even these silicone gels have a high original hardness and thus increase the force pushing up the chip, resulting in cracks or breakage of the flip-chips or breakage of the soldering bumps. Accordingly, these silicone gels limit the size of a chip which can be used.